High-molecular, cross-linked polyvinyl butyrals, method for the production thereof and their use

ABSTRACT

The present invention relates to high-molecular-weight, crosslinked polyvinyl butyrals obtainable by crosslinking a polyvinyl butyral with at least one di- and/or polycarboxylic acid or derivatives of these as crosslinking reagent, to a process for their production, and to their use.

This is a U.S. National Phase Application Under 35 USC 371 and applicantherewith claims the benefit of priority of PCT/EP01/04259 filed Apr. 12,2001, which was published Under PCT Article 21(2) in German, and GermanApplication No. 100 18 517.7 filed Apr. 13, 2000.

The present invention relates to novel high-molecular-weight crosslinkedpolyvinyl butyrals, a process for their production, and their use.

It is known that polyvinyl butyrals can be extruded together withplasticizers to give films used in particular in laminated safety glass.

To increase the molecular weight of polyvinyl butyrals of this type,EP-A-0 211 818 proposes crosslinking polyvinyl butyrals via stableintermolecular diacetal links. The crosslinking takes place viaaldehydes having at least two aldehyde groups. The crosslinker here isadded prior to or during the acetalization of the polyvinyl alcoholswith butyraldehyde.

However, due to the high reactivity of the aldehydes, crosslinking ofpolyvinyl butyrals with dialdehydes gives polyvinyl butyrals which arehighly crosslinked and of very high molecular weight, and which aretherefore not always soluble. In addition, low selectivity means thatthe crosslinking reaction is difficult to control, and it is thereforevery difficult to produce products of reproducible quality.

The object of the present invention was therefore to provide polyvinylbutyrals whose mechanical strength is higher than non-crosslinkedproducts and which, in addition, can be prepared reproducibly.

Surprisingly, it has been found that high-molecular-weight polyvinylbutyrals can be prepared reproducibly by crosslinking with di- and/orpolycarboxylic acids or with esters of these.

The present invention therefore provides high-molecular-weight,crosslinked polyvinyl butyral obtainable by crosslinking a polyvinylbutyral with at least one di- and/or polycarboxylic acid or withderivatives, preferably esters, of these as crosslinking reagent.

Preferred crosslinking agents are oxalic acid, malonic acid, succinicacid, glutaric acid, adipic acid, maleic acid, fumaric acid, itaconicacid, phthalic acid, terephthalic acid, and also esters of these.

Particularly preferred crosslinking reagents are aliphatic diesters ofthe formula (I)

ROOC—(CH₂)_(n)—COOR  (I)

where the radicals R are identical or different and, independently ofone another, are C₁-C₄-alkyl, and n is from 0 to 4, preferably 0.

Use is made particularly of diethyl and/or dimethyl oxalate.

The crosslinked polyvinyl butyrals therefore have the followingstructural units:

P—OOC—(CH₂)_(n)—COO—P

where n is from 0 to 4, and P is each of the polyvinyl butyral chains.

The polyvinyl butyrals of the invention have chemical strength markedlyhigher than that of conventional products.

The starting materials used may be any of the polyvinyl butyrals knownto the skilled worker, and there is therefore no restriction of any kindon the molecular weight of the starting polyvinyl butyrals. However,preference is given to polyvinyl butyrals with a molar mass of at least50 000 g/mol. The polyvinyl alcohol contents of the polyvinyl butyralsused as starting materials are preferably from 10 to 25% by weight, andparticularly preferably from 16 to 23% by weight. The polyvinyl acetatecontents of the polyvinyl butyrals used as starting materials arepreferably from 0 to 20% by weight.

In one preferred embodiment, the high-molecular-weight, crosslinkedpolyvinyl butyrals prepared according to the invention compriseplasticizer or plasticizer mixtures. The plasticizers used here may beany of the plasticizers known to the skilled worker, in particularesters of polybasic acids, of polyhydric alcohols, or of oligoetherglycols. Examples of preferred plasticizers are diesters of aliphaticdiols, or of aliphatic polyether diols, or of polyether polyols, withaliphatic carboxylic acids, preferably diesters of polyalkylene oxides,in particular diesters of di-, tri- or tetraethylene glycol withaliphatic C₆-C₁₀ carboxylic acids, or else diesters of aliphatic oraromatic C₂-C₁₈ dicarboxylic acids with aliphatic C₄-C₁₂ alcohols,preferably dihexyl adipate, or else mixtures of the esters mentioned.The amounts of the plasticizer used are the usual amounts known to theskilled worker, and the plasticizer content here is preferably from 25to 60 parts by weight, based on 100 parts by weight of PVB.

The present invention therefore also provides a process for preparingthe polyvinyl butyrals of the invention, which comprises adding thecrosslinking reagent, and also, where appropriate, the plasticizer, tothe polyvinyl butyral, homogenizing the mixture, where appropriate, andthermally crosslinking the same at temperatures within the range from 80to 280° C.

In one preferred embodiment, the crosslinking is catalyzed by addingalkaline or acidic additives.

Examples of alkaline or acidic additives which may be used are thehydroxides, alkanoates, carboxylates, sulfates, chlorides, nitrates, orphosphates of alkali metals and/or of alkaline earth metals, and freeorganic and/or inorganic acids, and amines.

The preparation of the high-molecular-weight, crosslinked polyvinylbutyrals of the invention is described below in greater detail in onepreferred embodiment, but without limitation thereto.

The crosslinking reagent may be in dissolved form, for example in theplasticizer, when added to the polyvinyl butyral, and the mixture maythen be homogenized.

The concentration of the crosslinking reagent here is preferably in therange from 0.01 to 10% by weight, particularly preferably in the rangefrom 0.1 to 3% by weight, and in particular in the range from 0.1 to 1%by weight, based in each case on polyvinyl butyral.

The thermal crosslinking may be carried out in any of the heatableassemblies known to the skilled worker, e.g. kneaders or autoclaves.However, the crosslinking preferably takes place in an extruder, andindeed preferably at melt temperatures in the range from 80 to 280° C.

The crosslinking reaction is promoted by the polymer alkalinity usuallyestablished so as to stabilize the polyvinyl butyral.

The present application also provides a molding composition comprisingthe high-molecular-weight crosslinked polyvinyl butyral of theinvention.

The extrusion process described can also process the polyvinyl butyralof the invention directly to give a film, with the aid of a slot die.Processes for producing polyvinyl butyral films are well known to theskilled worker. Films made from he high-molecular-weight crosslinkedpolyvinyl butyrals of the invention may also comprise other conventionaladditives, e.g. oxidation stabilizers, UV stabilizers, dyes, pigments,and also release agents.

The present application therefore also provides a film comprising thehigh-molecular-weight, crosslinked polyvinyl butyral of the invention.

The films have high tear strength, particularly advantageous forproducing laminated safety glass, which is the main application sectorfor the films.

The present invention therefore also provides the use of the films ofthe invention for producing laminated safety glass.

The invention is described in detail below using examples, but withoutbeing restricted thereby

BRIEF DESCRIPTION OF THE DRAWINGS

Certain preferred embodiments are described below with reference to theaccompanying figures in which:

FIG. 1 is a schematic illustration of the orientation of test impacts.

FIG. 2 is a graphical illustration of the results of a standard pummeltest.

Test Methods

Polyvinyl Alcohol Content of PVB

For this test, the PVB is acetylated with an excess of acetic anhydridein pyridine. After the reaction, the excess acetic anhydride ishydrolyzed with water and the resultant solution is titratedpotentiometrically with sodium hydroxide solution. The PVOH content iscalculated from the amount of sodium hydroxide solution consumed.

Polyvinyl Acetate Content of PVB

For this test, the PVB is dissolved in a benzyl alcohol/ethanol mixture.The acetyl groups are saponified with an excess of alcoholic potassiumhydroxide. The excess potassium hydroxide solution is back-titrated withhydrochloric acid. The polyvinyl acetate content is calculated from theamount of hydrochloric acid consumed.

Mw, Mn

Molecular weights of the polyvinyl butyrals present in the moldingcompositions are determined by gel permeation chromatography (GPC) inglacial acetic acid using RI detectors. The detectors are calibrated bymeans of PVB calibration standards whose absolute values are determinedby means of static light scattering.

Alkaline Titer of PVB

For this test, the PVB is dissolved in ethanol and titrated with 0.01molar hydrochloric acid until the color changes from green to violet.The indicator used is a mixture of methylene blue and neutral red. Thealkaline titer is calculated from the amount of hydrochloric acidconsumed.

Tear Strength

For measuring tear strength, the films are stored under controlledconditions of temperature and humidity for 24 hours at 23° C. andrelative humidity of 50%. The tear strength is measured using a tensileand compressive strength test machine (manufacturer: Cadis GbR, model:BRP 201) to DIN 53455.

Melt Index

For measuring melt index, the films are stored under controlledconditions of temperature and humidity for 24 hours at 23° C. andrelative humidity of 50%. The measurements on the films are made using amelt index tester (manufacturer: Göttfert, model: MP-D) at 190° C. witha load of 2.16 kg and using a 2 mm die, to ISO 1133.

PVB Film Moisture Level

The moisture level in the PVB film is measured using an infraredphotometer (manufacturer: Pier-Electronic GmbH, Wallau), on laminatedsafety glass. The measurement device is calibrated in advance usingappropriate calibration standards.

Pummel

The test specimens for the pummel test are produced as follows: Thefilms are stored under controlled conditions of temperature and humidityfor 24 hours at 23° C./30% relative humidity. They are laminated to 2 mmfloat glass with F/F and Sn/Sn orientation of film to glass surface. Theglass is washed with demineralized water prior to coating. The laminatedpanes of glass are produced by compressing the composites in aprelamination oven using calender rolls at temperatures of from 40 to100° C. and then compressing the composites in an autoclave at apressure of 12 bar and at a temperature of 140° C. for 30 minutes.

Test specimens of dimensions 10×30 cm are cut from the resultantlaminated safety glass in order to carry out the pummel test. The testspecimens are held at −18° C. for 4 hours and then placed on a supporttilted at 45° and impacted with an automatic hammer until the glass hasbeen pulverized. The orientation of the impacts is as shown in FIG. 1.The results are evaluated using a standard pummel scale from 0 to 10, asshown in FIG. 2.

EXAMPLES Comparative Example 1

Mixture

370 g of polyvinyl butyral (polyvinyl alcohol content=18.9% by weight,polyvinyl acetate content=1.1% by weight, alkaline titer=16 ml of 0.01MHCI/100 g) are mixed with 130 g of triethylene glycol bis(2-heptanoate)(3G7). The mixing takes place in a laboratory mixer (manufacturer:Papenmeier, model TGHKV20/KGU63; Brabender, model 826801). Prior topreparing the mixture, 0.75 g of Tinuvin® P (UV stabilizer,manufacturer: Ciba Specialty Chemicals) is dissolved in the plasticizer.The PVB/plasticizer mixtures are used to extrude flat films of thickness0.8 mm.

Extrusion

Extrusion takes place in a twin-screw extruder with counter-rotatingscrews (manufacturer: Haake) equipped with melt pump and slot die, at amelt temperature of 190° C.

Example 1

Mixing and extrusion takes place as in comparative example 1. However,besides the UV stabilizer, 2.22 g of diethyl oxalate crosslinkingreagent are also dissolved in the plasticizer.

Comparative Example 2

Mixing and extrusion take place as in example 1. Instead of the PVB usedin comparative example 1, use is made of 370 of a polyvinyl butyral witha polyvinyl alcohol content of 20.9% by weight and a polyvinyl acetatecontent of 1.1% by weight, and with an alkaline titer of 16 ml of 0.01MHCl/100 g.

Example 2

Mixing and extrusion take place as in comparative example 1. Instead ofthe PVB used in comparative example 1,370 g of the polyvinyl butyral ofcomparative example 2 are used. Besides the UV stabilizer, 2.22 g ofdiethyl oxalate crosslinking reagent are also dissolved in theplasticizer, as in example 1.

Comparative Example 3

Mixing and extrusion takes place as in comparative example 1. However,374.5 g of the polyvinyl butyral from comparative example 1 are used.Instead of the plasticizer (3G7) used in comparative example 1,215.5 gof dihexyl adipate (DHA) are used.

Example 3

Mixing takes place as in comparative example 3 and extrusion as incomparative example 1. However, besides the UV stabilizer 2.22 g ofdiethyl oxalate crosslinking reagent are also dissolved in theplasticizer, as in example 1.

Comparative Example 4

Mixture 2247 g of polyvinyl butyral (polyvinyl alcohol content=20.6% byweight, polyvinyl acetate content=1.1% by weight, alkaline titer=21 mlof 0.01M HCl/100 g) are mixed with 753 g of dihexyl adipate. Mixingtakes place in a laboratory mixer (manufacturer: Papenmeier, modelTGHKV20/KGU63; Brabender, model 826801). Prior to preparing the mixture,4.5 g of Tinuvin® P (UV stabilizer, manufacturer: Ciba SpecialtyChemicals) are dissolved in the plasticizer. The PVB/plasticizermixtures are used to extrude flat films of thickness 0.8 mm.

Extrusion

Extrusion takes place in a twin-screw extruder with corotating screws(manufacturer: Leistritz) equipped with melt pump and slot die, at amelt temperature of 200° C.

Example 4a

Mixing and extrusion take place as in comparative example 4. However,besides the UV stabilizer, 6.74 g of diethyl oxalate crosslinkingreagent are also dissolved in the plasticizer.

Example 4b

Mixing and extrusion take place as in comparative example 4. However,besides the UV stabilizer, 5.3 g of diethyl oxalate crosslinking reagentare also dissolved in the plasticizer.

Example 4c

Mixing takes place as in example 4b and extrusion as in comparativeexample 4. An alkaline titer of 77 ml of 0.01M HCl/100 g is also appliedto the PVB by means of aqueous potassium hydroxide solution, prior tomixing with the plasticizer.

Example 4d

Mixing takes place as in example 4 and extrusion as in comparativeexample 4. However, 10.6 g of dimethyl oxalate are used instead of 5.3g.

Comparative Example 5

Mixture

2220 g of polyvinyl butyral (polyvinyl alcohol content=20.6% by weight,polyvinyl acetate content=1.1% by weight, alkaline titer=21 ml of 0.01MHCl/100 g) with 780 g of triethylene glycol bis(2-heptanoate). Mixingtakes place in a laboratory mixer (manufacturer: Papenmeier, modelTGHKV20/KGU63; Brabender, model 826801). Prior to preparing the mixture,4.5 g of Tinuvin® P (UV stabilizer, manufacturer: Ciba SpecialtyChemicals) are dissolved in the plasticizer. The PVB/plasticizermixtures are used to extrude flat films of thickness 0.8 mm.

Extrusion

Extrusion takes place in a twin-screw extruder with corotating screws(manufacturer: Leistritz) equipped with melt pump and slot die, at amelt temperature of 200° C.

Example 5

Mixing and extrusion take place as in comparative example 5. However,besides the UV stabilizer, 5.24 g of dimethyl oxalate crosslinkingreagent are also dissolved in the plasticizer.

The examples confirm that polyvinyl butyral can be thermally crosslinkedusing derivatives of dicarboxylic acids. The increase in molecularweight through the effect of the crosslinking reagents is detectablefrom the rise in the molecular weights Mw and Mn, and also from the fallin the melt index values. The crosslinking reaction is promoted byraising the alkaline titer of the polyvinyl butyral used (cf.comparative example 4 and examples 4b and 4c), and also by risingconcentration of the crosslinker (cf. comparative example 4 and examples4d and 4c). The crosslinking reaction improves the mechanical propertiesof films produced from the molding compositions, and this is detectablefrom the rise in tear strengths. The glass adhesion of the films isessentially unaffected by the crosslinking reaction, and this isdetectable from the pummel values and is an important precondition forthe use of the films in laminated safety glass.

Comparative Comparative Comparative Example example 1 Example 1 example2 Example 2 example 3 Example 3 Polyvinyl alcohol content of startingPVB [%] 18.9 18.9 20.9 20.9 18.9 18.9 Polyvinyl acetate content ofstarting PVB [%] 1.1 1.1 1.1 1.1 1.1 1.1 Alkaline titer of starting PVB[ml of 0.01M 16 16 16 16 16 16 HCI/100 g] Plasticizer 3G7 3G7 3G7 3G7DHA DHA Crosslinking reagent none diethyl oxalate none diethyl oxalatenone diethyl oxalate Tear strength [N/mm²] 26.39 27.27 28.05 29.67 26.8527.77 MFI 190 [g/10 min] 2.81 2.69 4.00 1.83 3.90 3.30 Film moisturelevel [%] 0.44 0.44 0.49 0.48 0.40 0.40 Pummel F 8 7-8 8 8 7 6-7 PummelSn 4 3-4 4 3 4 4 Comparative Comparative Example example 4 Example 4aExample 4b Example 4c Example 4d example 5 Example 5 Polyvinyl alcoholcontent of starting PVB [%] 20.6 20.6 20.6 20.6 20.6 20.6 20.6 Polyvinylacetate content of starting PVB [%] 1.1 1.1 1.1 1.1 1.1 1.1 1.1 Alkalineliter of starting PVB 21 21 21 77 77 21 21 [ml of 0.01M HCI/100 g]Plasticizer DHA DHA DHA DHA DHA 3G7 3G7 Crosslinking reagent nonediethyl dimethyl dimethyl dimethyl none dimethyl oxalate oxalate oxalateoxalate oxalate Tear strength [N/mm²] 30.77 32.80 32.46 32.37 32.9028.28 28.44 MFI 190 [g/10 min] 2.39 1.75 1.73 0.78 0.46 2.28 0.54 Mw ofPVB after extrusion [g/mol] 104050 113300 142400 154100 Mn of PVB afterextrusion [g/mol] 54200 60100 61150 48600 Mw/Mn 1.92 1.89 2.33 3.11 Filmmoisture level [% ] 0.45 0.45 0.44 0.44 0.44 0.49 0.46 Pummel F 7-8 8 88 9 6 6 Pummel Sn 5-6 5 5 5 4-5 4 4

What is claimed is:
 1. A high-molecular-weight, crosslinked polyvinylbutyral obtained by crosslinking a polyvinyl butyral with at least onealiphatic diester of the formula (I): ROOC—(CHA—COOR  (I) ascrosslinking reagent, where the radicals R are identical or differentand, independently of one another, are C1-C4-alkyl, and n is from 0 to4.
 2. The polyvinyl butyral as claimed in claim 1, wherein diethyland/or dimethyl oxylate are used as crosslinking reagents.
 3. Thepolyvinyl butyral as claimed in claim 1, which comprises plasticizer. 4.A process for preparing a polyvinyl butyral as claimed in any one of thepreceding claims, which comprises adding the crosslinking reagent, andalso, where appropriate, the plasticizer, to the polyvinyl butyral,homogenizing the mixture, where appropriate, and thermally crosslinkingthe same at temperatures in the range from 80 to 280° C.
 5. The processas claimed in claim 4, wherein the crosslinking is catalyzed by addingalkaline or acidic additives.
 6. The process as claimed in claim 4,wherein the thermal crosslinking is carried out in an extruder.
 7. Amethod for preparing molding compositions comprising using a polyvinylbutyral as claimed in any one of claims 1 to
 3. 8. A method forproducing films comprising using a polyvinyl butyral as claimed in anyone of claims 1 to
 3. 9. A film comprising a polyvinyl butyral asclaimed in any one of claims 1 to
 3. 10. A method for producinglaminated safety glass comprising using a film as claimed in claim 9.